# fastjson2
**Repository Path**: alibaba/fastjson2
## Basic Information
- **Project Name**: fastjson2
- **Description**: π FASTJSON2 is a Java JSON library with excellent performance.
- **Primary Language**: Unknown
- **License**: Apache-2.0
- **Default Branch**: main
- **Homepage**: None
- **GVP Project**: No
## Statistics
- **Stars**: 56
- **Forks**: 13
- **Created**: 2024-10-31
- **Last Updated**: 2026-10-11
## Categories & Tags
**Categories**: json-tools
**Tags**: None
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##### Language: English | [δΈζ](README_cn.md)
# FASTJSON 2
**FASTJSON 2** is a high-performance JSON library for Java, designed as the next-generation successor to FASTJSON with a goal of providing an optimized JSON solution for the next ten years.
## Highlights
- **Blazing Fast** - Significantly outperforms Jackson, Gson, and org.json. [Benchmarks](https://github.com/alibaba/fastjson2/wiki/fastjson_benchmark)
- **Dual Format** - Native support for both JSON (text) and [JSONB (binary)](https://alibaba.github.io/fastjson2/JSONB/jsonb_format_en) protocols
- **Full & Partial Parsing** - Complete document parsing or selective extraction via [JSONPath](https://alibaba.github.io/fastjson2/JSONPath/jsonpath_en) (SQL:2016 compatible)
- **Modern Java** - Optimized for JDK 8/11/17/21 with compact string, Record, and Vector API support
- **Multi-Platform** - Works on Java servers, Android 8+ clients, and big data pipelines
- **Kotlin Native** - First-class [Kotlin extensions](https://alibaba.github.io/fastjson2/Kotlin/kotlin_en) with idiomatic DSL-style API
- **JSON Schema** - Built-in [validation support](https://alibaba.github.io/fastjson2/JSONSchema/json_schema_en) with high performance
- **Secure by Default** - AutoType disabled by default; no hardcoded whitelist; SafeMode support
- **GraalVM Ready** - Compatible with GraalVM Native Image
## Table of Contents
- [Quick Start](#quick-start)
- [Installation](#1-installation)
- [Core Library](#11-core-library)
- [Fastjson v1 Compatibility](#12-fastjson-v1-compatibility-module)
- [Kotlin Module](#13-kotlin-module)
- [Spring Integration](#14-spring-framework-integration)
- [Basic Usage](#2-basic-usage)
- [Parse JSON to JSONObject](#21-parse-json-to-jsonobject)
- [Parse JSON to JSONArray](#22-parse-json-to-jsonarray)
- [Parse JSON to Java Object](#23-parse-json-to-java-object)
- [Serialize to JSON](#24-serialize-java-object-to-json)
- [JSONObject & JSONArray](#25-working-with-jsonobject-and-jsonarray)
- [Serialize JavaBean](#26-serialize-javabean-to-json)
- [Advanced Usage](#3-advanced-usage)
- [JSONB Binary Format](#31-jsonb-binary-format)
- [JSONPath](#32-jsonpath)
- [Features Configuration](#33-features-configuration)
- [Annotations](#34-annotations)
- [Custom Serializer/Deserializer](#35-custom-serializerdeserializer)
- [Filters](#36-filters)
- [Upgrading from Fastjson 1.x](#4-upgrading-from-fastjson-1x)
- [Documentation](#5-documentation)
- [Contributing](#6-contributing)
## Quick Start
Add the dependency and start parsing JSON in seconds:
```xml
com.alibaba.fastjson2
fastjson2
2.0.65
```
```java
import com.alibaba.fastjson2.JSON;
// Parse
User user = JSON.parseObject("{\"name\":\"John\",\"age\":25}", User.class);
// Serialize
String json = JSON.toJSONString(user);
```
# 1. Installation
## 1.1 Core Library
The `groupId` for FASTJSON 2 is `com.alibaba.fastjson2` (different from 1.x):
**Maven:**
```xml
com.alibaba.fastjson2
fastjson2
2.0.65
```
**Gradle:**
```groovy
dependencies {
implementation 'com.alibaba.fastjson2:fastjson2:2.0.65'
}
```
> Find the latest version on [Maven Central](https://search.maven.org/artifact/com.alibaba.fastjson2/fastjson2).
## 1.2 Fastjson v1 Compatibility Module
If you are migrating from `fastjson 1.2.x`, you can use the compatibility package as a drop-in replacement. Note that 100% compatibility is not guaranteed - please test thoroughly and [report issues](https://github.com/alibaba/fastjson2/issues).
**Maven:**
```xml
com.alibaba
fastjson
2.0.65
```
**Gradle:**
```groovy
dependencies {
implementation 'com.alibaba:fastjson:2.0.65'
}
```
## 1.3 Kotlin Module
For projects using Kotlin, the `fastjson2-kotlin` module provides idiomatic Kotlin extensions:
**Maven:**
```xml
com.alibaba.fastjson2
fastjson2-kotlin
2.0.65
```
Add the Kotlin standard library and reflection library as needed. The reflection library is required when using data classes or constructor-based parameter passing:
```xml
org.jetbrains.kotlin
kotlin-stdlib
${kotlin-version}
org.jetbrains.kotlin
kotlin-reflect
${kotlin-version}
```
**Kotlin Gradle:**
```kotlin
dependencies {
implementation("com.alibaba.fastjson2:fastjson2-kotlin:2.0.65")
implementation("org.jetbrains.kotlin:kotlin-stdlib:$kotlin_version")
implementation("org.jetbrains.kotlin:kotlin-reflect:$kotlin_version")
}
```
## 1.4 Spring Framework Integration
For Spring Framework projects, use the appropriate extension module. See the full [Spring Integration Guide](docs/Spring/spring_support_en.md) for details.
**Maven (Spring 5.x):**
```xml
com.alibaba.fastjson2
fastjson2-extension-spring5
2.0.65
```
**Maven (Spring 6.x):**
```xml
com.alibaba.fastjson2
fastjson2-extension-spring6
2.0.65
```
**Gradle:**
```groovy
dependencies {
// Choose one based on your Spring version:
implementation 'com.alibaba.fastjson2:fastjson2-extension-spring5:2.0.65'
// or
implementation 'com.alibaba.fastjson2:fastjson2-extension-spring6:2.0.65'
}
```
# 2. Basic Usage
> The package name for FASTJSON 2 is `com.alibaba.fastjson2`. If upgrading from v1, simply update the package imports.
## 2.1 Parse JSON to `JSONObject`
**Java:**
```java
String text = "{\"id\":1,\"name\":\"fastjson2\"}";
JSONObject data = JSON.parseObject(text);
byte[] bytes = text.getBytes(StandardCharsets.UTF_8);
JSONObject data = JSON.parseObject(bytes);
```
**Kotlin:**
```kotlin
import com.alibaba.fastjson2.*
val text = """{"id":1,"name":"fastjson2"}"""
val data = text.parseObject()
val bytes: ByteArray = text.toByteArray()
val data = bytes.parseObject() // JSONObject
```
## 2.2 Parse JSON to `JSONArray`
**Java:**
```java
String text = "[{\"id\":1},{\"id\":2}]";
JSONArray data = JSON.parseArray(text);
```
**Kotlin:**
```kotlin
import com.alibaba.fastjson2.*
val text = """[{"id":1},{"id":2}]"""
val data = text.parseArray() // JSONArray
```
## 2.3 Parse JSON to Java Object
**Java:**
```java
String text = "{\"id\":1,\"name\":\"John\"}";
User user = JSON.parseObject(text, User.class);
```
**Kotlin:**
```kotlin
import com.alibaba.fastjson2.*
val text = """{"id":1,"name":"John"}"""
val user = text.to() // User
val user = text.parseObject() // User (alternative)
```
## 2.4 Serialize Java Object to JSON
**Java:**
```java
User user = new User(1, "John");
String text = JSON.toJSONString(user); // String output
byte[] bytes = JSON.toJSONBytes(user); // byte[] output
```
**Kotlin:**
```kotlin
import com.alibaba.fastjson2.*
val user = User(1, "John")
val text = user.toJSONString() // String
val bytes = user.toJSONByteArray() // ByteArray
```
## 2.5 Working with `JSONObject` and `JSONArray`
### 2.5.1 Get Simple Properties
```java
String text = "{\"id\": 2, \"name\": \"fastjson2\"}";
JSONObject obj = JSON.parseObject(text);
int id = obj.getIntValue("id");
String name = obj.getString("name");
```
```java
String text = "[2, \"fastjson2\"]";
JSONArray array = JSON.parseArray(text);
int id = array.getIntValue(0);
String name = array.getString(1);
```
### 2.5.2 Get JavaBean from JSON Containers
**Java:**
```java
JSONArray array = ...;
JSONObject obj = ...;
User user = array.getObject(0, User.class);
User user = obj.getObject("key", User.class);
```
**Kotlin:**
```kotlin
val array: JSONArray = ...
val obj: JSONObject = ...
val user = array.to(0)
val user = obj.to("key")
```
### 2.5.3 Convert JSONObject/JSONArray to JavaBean
**Java:**
```java
JSONObject obj = ...;
JSONArray array = ...;
User user = obj.toJavaObject(User.class);
List users = array.toJavaList(User.class);
```
**Kotlin:**
```kotlin
val obj: JSONObject = ...
val array: JSONArray = ...
val user = obj.to() // User
val users = array.toList() // List
```
## 2.6 Serialize JavaBean to JSON
**Java:**
```java
class User {
public int id;
public String name;
}
User user = new User();
user.id = 2;
user.name = "FastJson2";
String text = JSON.toJSONString(user);
byte[] bytes = JSON.toJSONBytes(user);
```
**Kotlin:**
```kotlin
class User(
var id: Int,
var name: String
)
val user = User(2, "FastJson2")
val text = user.toJSONString() // String
val bytes = user.toJSONByteArray() // ByteArray
```
Output:
```json
{"id":2,"name":"FastJson2"}
```
# 3. Advanced Usage
## 3.1 JSONB Binary Format
JSONB is a high-performance binary JSON format that provides significantly faster serialization/deserialization and smaller payload sizes. See the [JSONB Format Specification](https://alibaba.github.io/fastjson2/JSONB/jsonb_format_en).
### Serialize to JSONB
```java
User user = ...;
byte[] bytes = JSONB.toBytes(user);
byte[] bytes = JSONB.toBytes(user, JSONWriter.Feature.BeanToArray); // Even more compact
```
### Parse JSONB
```java
byte[] bytes = ...;
User user = JSONB.parseObject(bytes, User.class);
User user = JSONB.parseObject(bytes, User.class, JSONReader.Feature.SupportArrayToBean);
```
## 3.2 JSONPath
JSONPath enables partial parsing of JSON documents without full deserialization, which is ideal for extracting specific fields from large payloads. FASTJSON 2 implements [SQL:2016](https://en.wikipedia.org/wiki/SQL:2016) JSONPath syntax.
### Extract from String
```java
String text = ...;
JSONPath path = JSONPath.of("$.id"); // Cache and reuse for better performance
JSONReader parser = JSONReader.of(text);
Object result = path.extract(parser);
```
### Extract from byte[]
```java
byte[] bytes = ...;
JSONPath path = JSONPath.of("$.id"); // Cache and reuse for better performance
JSONReader parser = JSONReader.of(bytes);
Object result = path.extract(parser);
```
### Extract from JSONB byte[]
```java
byte[] bytes = ...;
JSONPath path = JSONPath.of("$.id"); // Cache and reuse for better performance
JSONReader parser = JSONReader.ofJSONB(bytes); // Note: use ofJSONB method
Object result = path.extract(parser);
```
See the full [JSONPath Documentation](https://alibaba.github.io/fastjson2/JSONPath/jsonpath_en) for filter expressions, aggregate functions, array slicing, and more.
## 3.3 Features Configuration
FASTJSON 2 provides fine-grained control over serialization and deserialization behavior through `JSONWriter.Feature` and `JSONReader.Feature`. All features are **OFF by default**.
```java
// Serialization with features
String json = JSON.toJSONString(user,
JSONWriter.Feature.WriteNulls,
JSONWriter.Feature.PrettyFormat);
// Deserialization with features
User user = JSON.parseObject(json, User.class,
JSONReader.Feature.SupportSmartMatch);
```
See the full [Features Reference](docs/features_en.md) for all available options and migration mapping from fastjson 1.x.
## 3.4 Annotations
Use `@JSONField` and `@JSONType` to customize serialization/deserialization behavior:
```java
public class User {
@JSONField(name = "user_name", ordinal = 1)
public String name;
@JSONField(format = "yyyy-MM-dd", ordinal = 2)
public Date birthday;
@JSONField(serialize = false)
public String password;
}
```
See the full [Annotations Guide](docs/annotations_en.md).
## 3.5 Custom Serializer/Deserializer
Implement `ObjectWriter` or `ObjectReader` for custom serialization logic:
```java
// Custom writer
class MoneyWriter implements ObjectWriter {
public void write(JSONWriter jsonWriter, Object object, Object fieldName, Type fieldType, long features) {
Money money = (Money) object;
jsonWriter.writeString(money.getCurrency() + " " + money.getAmount());
}
}
// Register
JSON.register(Money.class, new MoneyWriter());
```
See the full [Custom Reader/Writer Guide](docs/register_custom_reader_writer_en.md).
## 3.6 Filters
FASTJSON 2 provides a comprehensive filter system for serialization:
| Filter | Purpose |
|--------|---------|
| `ValueFilter` | Transform property values |
| `NameFilter` | Rename properties |
| `PropertyFilter` | Include/exclude properties conditionally |
| `AfterFilter` / `BeforeFilter` | Inject additional content |
| `LabelFilter` | Scenario-based serialization |
| `ContextValueFilter` / `ContextNameFilter` | Context-aware transformations |
See the full [Filter Documentation](docs/Filter/index_en.md).
# 4. Upgrading from Fastjson 1.x
FASTJSON 2 provides both a compatibility mode (drop-in replacement) and a new API mode for upgrading. Key changes:
| Aspect | Fastjson 1.x | Fastjson 2.x |
|--------|-------------|-------------|
| Package | `com.alibaba.fastjson` | `com.alibaba.fastjson2` |
| GroupId | `com.alibaba` | `com.alibaba.fastjson2` |
| AutoType | Enabled with whitelist | Disabled by default (more secure) |
| Circular Reference | Detected by default | Not detected by default |
| Smart Match | On by default | Off by default |
| Default Features | Multiple features on | All features off |
See the full [Migration Guide](docs/fastjson_1_upgrade_en.md) for step-by-step instructions, API mapping table, and common issues.
# 5. Documentation
## Core References
| Document | Description |
|----------|-------------|
| [Features Reference](docs/features_en.md) | Complete list of JSONReader/JSONWriter features |
| [Annotations Guide](docs/annotations_en.md) | @JSONField, @JSONType, @JSONCreator usage |
| [Architecture](docs/ARCHITECTURE.md) | Internal architecture, design patterns, and class hierarchy |
| [FAQ](docs/FAQ_en.md) | Frequently asked questions and troubleshooting |
## Format & Protocol
| Document | Description |
|----------|-------------|
| [JSONB Format](https://alibaba.github.io/fastjson2/JSONB/jsonb_format_en) | Binary JSON format specification |
| [JSONB vs Hessian/Kryo](docs/JSONB/jsonb_vs_hessian_kryo_en.md) | Performance comparison with other binary formats |
| [JSONB Size Comparison](docs/JSONB/jsonb_size_compare_en.md) | Payload size comparison |
| [CSV Support](docs/csv_en.md) | CSV reading and writing support |
## JSONPath
| Document | Description |
|----------|-------------|
| [JSONPath Guide](docs/JSONPath/jsonpath_en.md) | Syntax, operators, and examples |
| [Multi-value JSONPath](docs/JSONPath/jsonpath_multi_en.md) | Multi-value extraction |
| [Typed JSONPath](docs/JSONPath/jsonpath_typed_en.md) | Type-safe JSONPath extraction |
| [JSONPath Benchmark](docs/JSONPath/jsonpath_benchmark_en.md) | Performance data |
## Integrations
| Document | Description |
|----------|-------------|
| [Spring Support](docs/Spring/spring_support_en.md) | Spring MVC, WebFlux, Data Redis, Messaging |
| [Kotlin Extensions](docs/Kotlin/kotlin_en.md) | Kotlin API and DSL |
| [Android Support](docs/Android/android_benchmark_en.md) | Android 8+ integration |
## Customization
| Document | Description |
|----------|-------------|
| [Custom Reader/Writer](docs/register_custom_reader_writer_en.md) | Implement ObjectReader/ObjectWriter |
| [MixIn Annotations](docs/mixin_en.md) | Inject annotations on third-party classes |
| [AutoType Security](docs/autotype_en.md) | AutoType mechanism and security configuration |
| [JSON Schema](docs/JSONSchema/json_schema_en.md) | Schema validation |
| [Filter System](docs/Filter/index_en.md) | Serialization filters |
## Migration & Performance
| Document | Description |
|----------|-------------|
| [v1 to v2 Migration](docs/fastjson_1_upgrade_en.md) | Upgrade guide with API mapping |
| [Performance Guide](docs/performance_en.md) | Tuning tips and best practices |
| [Benchmarks](https://github.com/alibaba/fastjson2/wiki/fastjson_benchmark) | Comprehensive benchmark results |
# 6. Contributing
We welcome contributions of all kinds - bug reports, feature requests, documentation improvements, and code contributions.
- See [CONTRIBUTING.md](CONTRIBUTING.md) for development setup, coding standards, and the pull request process
- See [CODE_OF_CONDUCT.md](CODE_OF_CONDUCT.md) for community guidelines
- See [SECURITY.md](SECURITY.md) for reporting security vulnerabilities
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